<select name="log_comb[]" style="width: 130px">
    <option value="With aditive" <?php if (count($log_comb)>0) { if (in_array('With aditive',$log_comb)) { echo "selected"; } } ?>>With aditive</option>
    <option value="Without aditive" <?php if (count($log_comb)>0) { if (in_array('Without aditive',$log_comb)) { echo "selected"; } } ?>>Without aditive</option>
</select>